Experimental phase diagram of a mixture consisting of non-polar achiral liquid crystal 2-(4"-pentylbiphenyl-4-yl)-5-hexylpyrimidine (BPP-65) and chiral non-mesogenic compound (R,R)bis-(1,1,1-trifluorooct-2-yl)-4,4"-terphenyldi-carboxylate (R-FODTA-6) was constructed. The phase diagram displays temperature and concentration regions of various mesophases existed in the mixture: cholesteric (N*), ferroelectric smectic C* (SmC*), ferrielectric (Ferri), isotropic (Iso) and crystalline (Cr). The ferrielectric phase was induced due to intermolecular interactions between BPP-65 and R-FODTA-6. Although, each of the individual components does not form this mesophase. The evidence of the ferrielectric phase induction in the binary mixtures is the presence of two phase transitions in electric field detected within the R-FODTA-6 concentration range from 33 to 60 mol. %. At R-FODTA-6 concentrations below 33 mol. %, only one phase transition in electric field is observed, which is typical for the ferroelectric smectic C* phase. The widest temperature range of the enantiotropic ferrielectric phase (from 14 to 62 degrees C) was established in the eutectic point of the binary mixture. It has been experimentally demonstrated for the first time that the ferrielectric phase is intermediate between solid crystal and ferroelectric smectic C* phase, rather than between antiferroelectric and ferroelectric phases, as it was reported over the past thirty years and therefore considered as the rule.

Smectic ferroelectric liquid crystals (FLCs) have the potential to be used as optical media for display and photonic devices operating in kilohertz frequency range. The orientational Kerr-effect within deformed helix ferroelectric mode (DHF-mode) of chiral FLCs allows smooth and hysteresis-free adjustment of the electrically controlled effective birefringence Delta n(eff)(E) (E, T). In this work the maximum achievable electrically controlled effective birefringence in the DHF-mode Delta n(eff)(E) (E-DHF, T) was studied for four different smectic C* liquid crystals: two ferroelectric (FLCs) and two ferrielectric (FiLCs) ones. The criteria for the experimental determination of the maximum electric field in the DHF-mode E-DHF were discussed, and the criterion of the constancy of dielectric susceptibility was selected. It has been experimentally demonstrated that for FLCs, a decreasing temperature dependence of Delta n(eff)(E) (E-DHF, T) is realized, while for FiLCs, a dependence with a maximum is observed, despite the fact that the dependencies of K-kerr (T) are qualitatively similar for FLCs and FiLC. The research results may be useful in the design of advanced liquid crystal devices for light phase modulation in the DHF-mode and may help refine or develop theoretical models describing the temperature behavior of electro-optical parameters in FLCs and FiLCs.

The effect of non-mesogenic chiral additives, such as (S,S)-bis-(1,1,1-trifluorooct-2-yl)-4,4"-terphenyl-dicarboxylate (FODTA-6) and (S,S)-(1-butoxy-1-oxopropan-2-yl)-[1,1':4'1"-terphenyl]-4,4 ''-dicarboxylate (SS-LACT-4), on the properties of ferrielectric liquid crystal (FiLC) mixtures FerriLCM-1 and FerriLCM-2 was investigated. FODTA-6 induced a positive sign for spontaneous polarization and handedness in mixtures of polar smectic C* liquid crystals, while SS-LACT-4 induced a positive sign for spontaneous polarization but a negative sign for handedness. A non-chiral smectic C liquid crystal 2-(4'pentylbiphenyl-4'-yl)-5-hexyl pyrimidine (BPP-65) was used as a matrix. It was found that the absence of the chiral SS-LACT-4 dopant in FerriLCM-2 mixture resulted in a significant change of dielectric and electro-optical properties of the FiLC. In FerriLCM-2 mixture, several parameters decreased compared to viscosity, electric susceptibility, and orientational Kerr-effect coefficient kerrK . At the same time the electric critical fields 1cpE and 2cpE significantly increased. Within the framework of the existing phenomenological theory of chiral smectics C*, a quadratic dependence between orientational Kerr-effect coefficient and free relaxation time of helical structure was obtained. This quadratic relationship has been experimentally confirmed, yet it was also demonstrated that there are significant quantitative discrepancies between experimental data and theoretical calculations for FiLCs.

A clearly expressed effect of unpolarized light electro-optical modulation by homeoplanar structures of a smectic C* ferroelectric liquid crystal (FLC) and a ferrielectric liquid crystal (FerriLC) was discovered and investigated for the first time to our knowledge. This effect of electrically controlled light scattering is insensitive to the applied voltage sign, as for polymer-dispersed nematic liquid crystals (PDLCs), but the electro-optical modulation frequency reaches the kilohertz range. Occurrence conditions and essential features of the effect, as well as its physical origin, are discussed.

Broad temperature range ferrielectric liquid crystal mixture FerriLCM-1 was previously developed in 2022 (Pozhidaev et al. 2022). In that work dielectric and electro-optical properties of the mixture were studied at room temperature. Electrically induced birefringence index reached 0.01 at a wavelength of 532 nm with response times of 300 mu s. In this paper we continue the FerriLCM-1 properties investigation in a wide temperature range from the room ones till the isotropic phase transition temperature. It is found that one of the critical electric fields is almost temperature independent, while the Kerr coefficient of quadratic electro-optical effect in deformed helix ferroelectric (DHF) mode grows with temperature increase. This leads to an increase in the depth of phase modulation. Another critical electric field decreases smoothly with temperature rising. At 47-50 degrees C two critical electric fields merge, while temperature dependencies of all other dielectric and electro-optical parameters of the mixture are continuous and smooth functions. At about 50 degrees C the maximum electrically induced birefringence in DHF-mode is Delta n(eff)(E) = 0.022 nder the applied electric field E 0.4 V/mu m and with 80 mu s response time. FerriLCM-1 mixture operating in the DHF-mode exhibits a giant Kerr coefficient of 1700 nm/V-2 (or even up to 2900 nm/V-2 at lambda= 400 nm) ) at the temperature of 85 degrees C combined with a 50 mu s response time. This is the highest value of K-kerr coefficient among liquid crystals. All these properties make ferrielectric liquid crystal mixture FerriLCM-1 suitable for solving various problems of phase modulation of light and use in low-voltage devices.

Broad temperature range ferrielectric liquid crystal mixture FerriLCM-1 was previously developed by us in 2022 [Opt. Lett., 47, 1598, (2022)]. In this paper, we studied the frequency dependence of dielectric susceptibility of this mixture, as well as two critical electrical fields that characterize the ferrielectric phase. Liquid crystal cells of different thickness (1.85, 8.2, 11.4 and 57 mu m) were examined at room temperature (23 degrees & Scy;). An increase in dielectric susceptibility was observed with an increase of cell thickness, while the value of the first critical electrical field decreased. It was shown that when the frequency and cell thickness increase, it become impossible to determine the value of the second critical electric field based on the field dependence on dielectric susceptibility. It was also shown for four different waveforms of applied voltage (alternating with an interval between pulses, rectangular, triangular, and sinusoidal) that there is practically no effect on the value of dielectric susceptibility. However, there is a noticeable effect on the frequency dispersion. These results are significant for the practical use of electro-optic phase modulators based on liquid crystalline ferrielectrics.

The results of the research in the field of the electro-optics of nematic and smectic (ferroelectric) liquid crystals, performed at the Lebedev Physical Institute of the Russian Academy of Sciences (FIAN), as well as their applications in modulation of the amplitude, phase, or scattering of laser radiation in electrically and optically controlled transparencies (spatial light modulators); holographic memory devices; wave-field formers and image converters (including three-dimensional ones); and recognition, sensor, and other laser technique devices, are presented.

The roughness parameter Rz and the anisotropy of the surface free energy (ASFE) of a rubbed polymer layer (aligning layer) bounding a ferroelectric smectic C * liquid crystal (FLC) in liquid crystal cells are measured. The dependences of the ASFE and Rz on the aligning layer thickness L are measured for the first time. The concept of the free energy anisotropy (FEA) of a rough surface layer is introduced for the first time. The dependence of the FEA of the rough surface layer on the aligning layer thickness is measured. It is experimentally shown that the polydomain FLC structure transformation in liquid-crystal cells into a monodomain one occurs as a threshold transition, when the FEA value of the rough aligning layer exceeds a certain critical value.

The possibility of using a ferrielectric liquid crystal as an electro-optic medium for a phase spatial light modulator has been investigated. The electro-optic characteristics of a ferrielectric liquid crystal are measured, and a numerical simulation of a 12-sector spiral phase plate based on this crystal is performed. It is found that, at a sub-kilohertz frequency of phase shift switching modulation by 2π, the investigated liquid-crystal ferrielectric is a lower voltage electro-optic medium for space–time light modulators in comparison with ferroelectric liquid crystals.

Статья посвящена крупному ученому и организатору науки, профессору Льву Михайловичу Блинову, посвятившему свою жизнь исследованию жидких кристаллов и организованных молекулярных структур. Лев Михайлович является основателем школы экспериментальных исследований органических пленок и жидких кристаллов в Советском Союзе, им воспитаны десятки молодых ученых, ставших кандидатами и докторами наук. Л.М. Блиновым написаны сотни научных статей, множество обзоров, монографий и учебников, читались лекции как в России, так и по всему миру. Кратко изложена биография Льва Михайловича, дан обзор его наиболее значимых достижений и отдельных публикаций, получивших широкий резонанс в научном сообществе. Приведены воспоминания учеников и коллег.

A liquid crystalline (LC) electro-optical modulator providing an electro-optical response time up to 400 nanoseconds with a modulation frequency up to 500 kHz has been developed. The ferroelectric liquid crystal FLC-576 obtained by us was used as the electro-optical medium of the modulator. Its helix pitch р0 is much smaller than wavelengths of visible light (р0 < 100 nm). The liquid crystal operates in the deformed helix ferroelectric mode (DHF-effect) under the action of electric fields. The controlling electric fields are less than a critical field of helix unwinding. At high frequencies of the control voltage (over 10 kHz), the heating of electro-optical cell by repolarization currents of FLC can occur up to the temperature of phase transition from ferroelectric to paraelectric phase, which leads to the cessation of electro-optical modulation. The work experimentally and theoretically examines the self-heating issues of electro-optical modulators depending on the liquid crystal layer thickness, frequency and strength of applied electric field. The heat removal conditions from the liquid crystal cell have been determined and experimentally implemented. Under these conditions the LC is in the smectic C* ferroelectric phase temperature range, which is necessary to provide electro-optical modulation in submegaherts diapason.

We report the development of chiral smectic C (SmC*) ferroelectric liquid crystals (FLCs) obtained by mixing of a nematic liquid crystal (NLC) as a host and chiral non-mesogenic dopants. The NLC is a binary eutectic mixture of phenyl- and biphenyl-pyrimidines, while chiral dopants belong to homologous series of secondary dilactates with terphenyldicarboxylate core. The induction in the mixtures not only the cholesteric phase, but also the wide temperature range ferroelectric SmC* phase with the helix pitch p0≈100 nm and the spontaneous polarization Ps about 70 nC/cm2 has been confirmed by dielectric, optical, and electro-optical measurements. The developed FLC mixtures are highly efficient for the deformed helix ferroelectric liquid crystal electro-optical mode because the mixtures combine mechanical stability (or mechanical shock resistance) of NLCs and kilohertz switching frequency (due to short helix pitch) of FLCs. These FLCs can be used to create various photonic devices, such as generators of vortex light fields and field-sequential color displays.

The problem of formation a reproducible spatially-uniform alignment of smectic С* ferroelectric liquid crystals (FLCs) in liquid-crystal (LC) cells has not been completely solved yet. We investigated aligning layers (anisotropic coatings) of different types (island and continuous). These layers contact with FLC in LC cells and form a selected direction for molecular orientation. It was investigated the influence of mechanical cycles numbers of rubbing polymer alignment layers made of polyvinyl alcohol and polyamide 66 on the optical quality of FLC cells to which electric field was not applied. It is shown that there is an optimal number of rubbing cycles for obtaining the best optical quality of FLC cells; the number of cycles is individual for each polymer alignment layer and coating type.

The origin of ferroelectricity in smectic liquid crystals is attributed to the chirality of their molecules. The chirality reduces the space symmetry and leads to the helical (helicoidal) spatial distribution of molecular axes in ferroelectric and antiferroelectric liquid crystals (FLCs and AFLCs), called a helical structure, or helical nanostructure, if its period is much less than any wavelength of visible light. Deformations of FLCs and AFLCs helical structures under the applied electric field E lead to the emergence of a number of specific electro-optical effects. This review analyzes the main results of experimental and theoretical studies of various electro-optical manifestations of FLCs and AFLCs helical nanostructures deformations, which are already used to develop displays and photonic devices of a new generation.(c) 2022 Elsevier B.V. All rights reserved.

A chiral smectic liquid crystal in which a ferrielectric phase with a helix pitch p0 less than 125 nm exists over a temperature range of at least from -3°C to +36°C has been developed. Such a wide temperature range (including room temperatures) of the ferrielectric phase with a subwavelength helix pitch has been achieved for the first time, to the best of our knowledge, which creates opportunities for the practical use of ferrielectric liquid crystals. A quadratic electro-optical effect caused by deformations of the helix in an electric field is observed in the ferrielectric phase, and the Kerr coefficient, which reaches almost 200 nm/V2, is significantly higher than the same coefficient for the blue phase and for the smectic C* phase, which means a higher sensitivity of the developed ferrielectric liquid crystal to the electric field. The electro-optical response time does not exceed 300 μs at room temperatures for this ferrielectric liquid crystal.

Extraction of spectral information using liquid crystal (LC) retarders has recently become a topic of great interest because of its importance for creating hyper- and multispectral images in a compact and inexpensive way. However, this method of hyperspectral imaging requires thick LC-layer retarders (50 µm–100 µm and above) to obtain spectral modulation signals for reliable signal reconstruction. This makes the device extremely slow in the case of nematic LCs (NLCs), since the response time of NLCs increases proportionally to the square of the LC-layer thickness, which excludes fast dynamic processes monitoring. In this paper, we explore two approaches for solving the speed problem: the first is based on the use of faster nanospiral ferroelectric liquid crystals as an alternative to NLCs, and the second is based on using a passive multiband filter and focuses on multispectral extraction rather than hyperspectral. A detailed comparative study of nematic and ferroelectric devices is presented. The study is carried out using a 9-spectral bands passive spectral filter, covering the visible and near-infrared ranges. We propose the concept of multispectral rather than hyperspectral extraction, where a small number of wavelengths are sufficient for specific applications.

The paper considers the possibility of controlling the alignment quality of helical nanostructures of ferroelectric liquid crystals (FLCs) within the concept of biaxial surface potential due to variation the FLCs helical pitch p0 and polymer aligning layers structures.

The ferrielectric liquid crystal (FerriLC) phase with the helix pitch po of about 100 nm was revealed in a broad temperature range from -3°C to + 35°C in a mixture containing an achiral smectic-C (SmC) biphenylpyrimidine and two non-mesogenic chiral diesters of 4,4”-terphenyl dicarboxylic acid.

We developed polymer-dispersed liquid crystals (PDLCs) that effectively scatter light both in the visible and near-infrared ranges simultaneously. Such PDLCs are characterized by an optimal size distribution of nematic liquid crystal droplets within 0.4 − 3 µm, which is achieved due to the specially selected copolymer, the elaborated liquid crystal material as well as the proper cooling mode from the isotropic phase. These PDLC films provide electrically controlled light scattering modulation in the spectral range 300 − 2300 nm with the response time around 10 ms.

In this paper we report the new experimental results on the rise of a liquid crystal in flat capillaries with inner photosensitive surfaces. The capillaries with different surface orientations were prepared by the use of the photo-alignment technique. Such a surface treatment makes it possible to eliminate the noncontrollable influence of a nanorelief on the wetting process, which takes place in the rubbing treatment technique previously used in similar experiments. The dynamics of the capillary rise of a nematic liquid crystal 5CB (4-cyano-4′-pentylbiphenyl) in vertical plane capillaries with photo-aligned substrates were studied for the first time. It was found that the stationary value of a contact angle weakly depends on the direction of a planar surface orientation relative to the direction of a capillary rise. It has been shown that the application of strong electric fields resulted in a decreasing of the contact angle. The results, obtained for the nematic liquid crystal, are compared with the results of an investigation of the capillary flow in a shock-free ferroelectric smectic phase.